Understanding How Mountains and Rivers Make Life Possible (image) Stanford University Share Print E-Mail Caption Stanford assistant professor Kate Maher holds up two different soil types. The soil on the left is young, dark and composed of more chemically reactive minerals. The sample on the right is older and made up of less reactive minerals such as clays. Credit Matthew Rothe Usage Restrictions None Share Print E-Mail Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.